Resonator system for discharge tubes



June 10, 1958 F. COETERIER 2,833,710

RESONATOR SYSTEM FOR DISCHARGE TUBES Filed March 13, 1953 INVENTOR FREDERIK COETERIER AGENT United States Patent RESONATOR SYSTEM FOR DISCHARGE TUBES Frederik Coeterier, Eindhoven, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application March 13, 1953, Serial No. 342,255

Claims priority, application Netherlands March 20, 1952 5 Claims. (Cl. 3155.51)

This invention relates to a resonator system for a discharge tube for ultra-high frequency oscillations, comprising a lecher wire system made up of two conductors having a length equal to an odd number of times a quarter operating wavelength, said conductors being fitted in a conductive box and connected at one end to each other and to the box-shaped conductor.

A resonator system of this type may inter alia be employed in generator circuit-arrangements for producing oscillations with a frequency of the order of 10,000 II1C./S. Such a generator circuit has, for example, been described in Philips Technical Review of September 1946. The frequency of the generated oscillations depends upon the length ,of the conductors of the lecher Wire system. With the desired wave form the voltages on said conductors are in anti-phase with respect to each other. However, a difficulty is experienced in .that the lecher wire system is also able to oscillate in a :manner such that the voltages of the conductors are in phase with each other. The resonance frequency of this wave form is the same as that with the first-mentioned manner of oscillation, since in both cases the system consists of a quarter wave length line short-circuited at one end. Hence, there is danger that, due to unavoidable structural dissymmetries energy passes over from one wave form to the other, thus superposing an in phase voltage on the anti-phase voltages. Said phenomenon involves instability of the generator and, moreover, its eficiency is adversely aifected.

In accordance with the invention said difliculty is avoided by fitting within the box-shaped conductor a second lecher wire system, both conductors of which are each connected at one end to the box-shaped conductor, which ends are situated diametrically opposed i. e. at different ends of the lecher wire system. The free ends of the conductors of the first lecher wire system are electrically coupledto the middle portions of the conductors of the second lecher wire system, for example connected conductively or coupled capacitively, and the length of the second lecher wire system is equal to where A is equal to the operating wave length, C denoting the capacity of each conductor per unit length relatively to the box-shaped conductor and K designating the mutual capacity of the conductors of the second lecher wire system per unit length. It has been found that said proportions involve a considerable input resistance measured between the middle portions of the conductors of the second lecher Wire system with respect to out-of-phase oscillations, so that the desired wave form on the first lecher system is practically not influenced by the presence of the second lecher wire system. On the other hand the impedance between the said middle portions and the boxshaped conductor is low in respect of in phase voltages to the effect of suppressing troublesome in phase oscillations at the operating frequency. One advantage of the method proposed is that the length of the second lecher wire system is small relatively to the wave length, for example equal to /6 wavelength or less and that said lecher system may be arranged symmetrically with respect to the other lecher wire system so that it can easily be housed within the box-shaped conductor.

In order that the invention may be readily carried into effect, an example will now be described in detail with reference to the accompanying drawing, in which- Fig. 1 shows diagrammaticaly in sectional side'view a generator tube for producing centimetric waves. A glass envelope 1 contains an electrode system comprising a box-shaped conductor 2 of rectangular cross-section and conductors 3, 4, 5 and 6.

Fig. 2. is a plan view of said electrode system, and

Fig. 3 is a cross-section of this system on the line lII-III. At the lower ends the conductors 3 and 4 are connected to the bottom of the box-shaped conductor 2 and jointly constitute a unilaterally short-circuited lecher wire system whose length corresponds to one quarter wavelength of the oscillations produced by the generator. The frequency of the generator mainly depends upon said lecher wire system. A voltage supply 13 is connected between the box-shaped conductor 2 and the cathode 7 so that the electrode system 2, 3, 4, 5 and 6 has a high positive voltage relatively to the cathode. Within the envelope 1, a brake-field electrode 12 is provided at the end of box 2 remote from the cathode 7, to which electrode 12 a negative voltage relatively to the cathode is supplied from source 14.

Electrons from the cathode 7 are formed into a beam by means known per so (not shown) and directed towards a number of apertures 8, 9, 10 and 11 which are provided in the electrodes 2, 3, and 4 and extend in line with one another between the cathode 7 and the brake-field electrode 12. It will be assumed that such a wave is produced in the electrode system that the electrodes 3 and 4 oscillate in anti-phase relatively to each other, the electrode 2 being at a constant potential. The electrons passing through the system 2, 3, 4, are velocity-modulated. Electrons reaching the aperture 8 at an instant at which the voltage of the electrode 3 is, for example, positive relatively to the conductor 2 are accelerated in the space between the conductors 2 and 3. The initial velocity of the electrons and the spacing between the conductors 2, 3 and 4 are chosen such that the electrons accelerated in the space between the conductors 2 and 3 traverse the space between the conductors 3, 4 and between the conductor 4 and the rear wall of conductor 2 respectively at such instances as to be further accelerated. Similarly, electrons reaching the aperture 8 when the electrode 3 is negative relatively to the box 2 are retarded by the resonator system. After leaving the aperture 11, the electrons are retarded in the space between the conductor box 2 and the brake-field electrode 12 and change direction, hence they pass anew through the apertures 11, 10, 9, 8 but now in the reverse direction. In the space between the box 2 and the brake-field electrode 12, the accelerated electrons have to travel a longer path compared with the retarded electrons, so that the beam .reflected by the electrode 12 is density-modulated. On passing through the resonator system in the direction from the electrode 12 to the cathode 7 the electrons give off energy to the resonator system to the effect of maintaining the initial wave, so that energy may be withdrawn from said system by means not shown in the drawing. The electron beam from the cathode 7 constitutes a source of an electric signal which is connected to the conductors 3 and 4 to apply the signal thereto in an out-of-phase manner. With the method of operation of the discharge tube as briefly stated above it has been postulated that Patented June 1 0, 1958- the resonator system vibrates in a manner such that the conductors 3 and 4 are consistently in anti-phase with respect to each other. Alternatively, however, the resonator system may vibrate such that the conductors 3 and 4 oscillate co-phasally with respect to the box-shaped conductor 2, the conductors 3 and 4 constituting as it were the internal conductors of a coaxial conductor whose external conductor is constituted by the box 2 and which is short-circuited at one end. The resonance frequency of this co-phasal oscillatory system is equal to that of the desired non co-phasal waveform, since in both cases there is a unilaterally short-circuited line of a quarter wavelength and the electric length is in both cases equal to the length of the conductors 3 and 4. Hence, there is a risk of the resonator being excited in the undesired waveform by the electrons or of energy of desired waveform being changed over to the undesired form due to the said mutual coupling. In this instance, an in phase voltage is superposed on to the anti-phase voltages on the conductors 3 and 4, owing to which the electrons no longer traverse the several spaces of the resonator system at the correct instants and the efficiency of the device is impaired. The co-phase waveform may moreover involve instability, for example skipping of the frequency or even release of the generator. In order to avoid said troublesome effects two further conductors 5 and 6 are fitted, within the box-shaped conductor 2, at right angles to the conductors 3 and 4, said conductors 5 and 6 extending parallel to each other and constituting another lecher wire system. The conductors 5 and 6 are connected at opposite ends 15 and 16 to the inner wall of the box-shaped conductor 2 and coupled capacitatively at their middles 17 and 18 to the free ends of the conductors 3 and 4. The length of the conductors 5 and 6 is equal to where A is equal to the wavelength of the oscillation produced, C denoting the capacity of each conductor per unit length relatively to the inner wall of the box-shaped conductor 2, and K denoting the mutual capacity per unit length of the conductors 5 and 6.

If, for example, the capacity C equalizes the mutual capacity K, the length of the conductors 5 and 6 is equal to /6 wavelength. The length of the conductors 5 and 6 may be reduced by placing them relatively closer together so that the capacity K exceeds the capacity C. In this connection it is pointed out that the conductors 5 and 6 need not be arranged in line with the conductors 3 and 4.

With the aforesaid proportions of the conductors 5 and 6 the input resistance of the lecher wire system 5, 6, measured between the middles 17 and 18, is practically infinite if the voltages are supplied in anti-phase to points 17 and 18, hence the desired anti-phase waveform on the lecher wire system 3, 4 is not influenced by the presence of conductors 5 and 6. However, the system 5, 6 has a low input resistance between points 17, 18 on the one hand and the box-shaped conductor 2 on the other hand with respect to in phase input voltages, so that the lecher wire system 3, 4 is highly capacitativelyloaded for in phase oscillations by the system 5, 6, and the resonance frequency for said oscillations is so far shifted as to avoid interaction of both waveforms. Although it is fundamentally possible for the middle portions of the conductors 5 and 6 to be conductively connected directly to the free ends of the conductors 3 and 4 it has, in practice,

been found that a capacitative coupling is preferable.

What is claimed is:

1. A resonator system comprising a conductive box, a first lecher line disposed in said box and provided with two conductors having a length equal to an odd multiple of a quarter wavelength of a predetermined wavelength, said two conductors of said first line each being connected at one end thereof to said box, a source of an electric signal, means connected to said two conductors to apply said signal out-of-phase to said two conductors, a second lecher line disposed in said box and provided with two wires, one end of one of said wires being connected to said box, an end of the other wire opposing said one end being connected to said box, and means coupling each of the free ends of the conductors to the mid-point of a respective wire, the length of said wires being equal to where A is equal to the operating wavelength, C denoting the capacity of each wire per unit length relatively to the said conductive box and K denoting the mutual capacity of the wires of the second lecher line per unit length.

2. A resonator system, as set forth in claim 1, wherein said conductive box has a rectangular cross-section, where-in said conductors of said first lecher line are arranged parallel to the side walls within said box and wherein said wires of said second lecher line extend in a plane at right angles to the axes of said conductors.

3. A resonator system, as set forth in claim 2, wherein said coupling means is constituted by a capacitive element.

4. A resonator system as claimed in claim 2, in which each of said conductors and opposed walls of said conductive box is provided with an aperture, said apertures being aligned on a common axis, and in which said source of electric signals comprises a source for producing an electron beam directed through said apertures, and a repelling electrode positioned in the path of said electron beam.

5. A resonator system comprising a box-like structure which is electrically conductive, a pair of conductors positioned in said box-like structure to form a first lecher line, corresponding ends of said conductors being connected to a wall of said box-like structure, a source of an electric signal, means connected to said conductors to apply said signal out-of-phase to said conductors, a pair of wires positioned in said box-like structure to form a second lecher line, opposed ends of said wires being respectively connected to said box-like structure, and means for respectively electrically coupling the remaining ends of said conductors to the middle portions of said wires.

References Cited in the file of this patent UNITED STATES PATENTS 

